8 Channel, 3U NEVE 1073 completed

Hey guys! Probably it was answered before but couldn't find exactly where.  When you separate PSU why would you need 4 cable  XLR?

1. +24V
2.0
3. +48v

What is 4-th used for?

Olegarich said:

Hey guys! Probably it was answered before but couldn't find exactly where.  When you separate PSU why would you need 4 cable  XLR?

1. +24V
2.0
3. +48v

What is 4-th used for?

Click to expand...

Using the four pin prevents plugging a standard XLR where the power should go. On my four channel build I actually have a 3 pin XLR for power, but I'm the only one using it and it stays plugged in and mounted in a rack.

Thanks!

Paul

Thank you Paul!

Hi,
I’m having a little issue getting 48v to work independently for 2 channels.  When 48v is on for one channel the  other channel gets power as well. At this point both channels are showing 33v.  Only when I turn 48v on for both channels do I get 48v.  Anyone else have this issue?  What have I missed?  Thank you 

tomnyhbees said:

Hi,
I’m having a little issue getting 48v to work independently for 2 channels.  When 48v is on for one channel the  other channel gets power as well. At this point both channels are showing 33v.  Only when I turn 48v on for both channels do I get 48v.  Anyone else have this issue?  What have I missed?  Thank you

Click to expand...

Are you hard wiring it or using a JLM Go Between?

Thanks!

Paul

Potato Cakes said:

Are you hard wiring it or using a JLM Go Between?

Thanks!

Paul

Click to expand...

Hard wiring.

Olegarich said:

Hey guys! Probably it was answered before but couldn't find exactly where.  When you separate PSU why would you need 4 cable  XLR?

1. +24V
2.0
3. +48v

What is 4-th used for?

Click to expand...

Like Potato explained, you need it foolproof, that way no one can accidentally connect a 3 pin audio XLR there or  to the PSU Output.

You don't need an XLR you can also use on of this connectors (a different type, not used in audio connections),
I think it's called a CB connector, it can be 3 pins, 4 pins or more

Potato Cakes said:

Are you hard wiring it or using a JLM Go Between?

Thanks!

Paul

Click to expand...

The issue  is the Neutrik metal connectors are conducting.  So that means the entire enclosure is getting 48v. 

tomnyhbees said:

The issue  is the Neutrik metal connectors are conducting.  So that means the entire enclosure is getting 48v.

Click to expand...

You should see +48V as referenced to 0V which ultimately should tie to a star ground point, which will be the chassis. But Pin 2 and 3 of the XLR should not have any continuity with the chassis, which is where you should have +48VDC from the phantom power switch connected via two 6k8 divider resistors.

I think you just need to do a thorough continuity test to see if you have any shorts. And also make sure that you are getting +48V at all of your phantom power switch poles when they are in the off position.

Thanks!

Paul

tomnyhbees said:

The issue is the Neutrik metal connectors are conducting. So that means the entire enclosure is getting 48v.

Click to expand...

What?
there's some confusion there...

3 pin Neutrik XLR metal connectors have 3 pins plus the metal case of the connector, neither of the 3 pins conduct to each other or to the metal case

48V phantom power is applied to Pin 2 and Pin 3 only

tomnyhbees said:

The issue  is the Neutrik metal connectors are conducting.  So that means the entire enclosure is getting 48v. 

Click to expand...

Potato Cakes said:

You should see +48V as referenced to 0V which ultimately should tie to a star ground point, which will be the chassis. But Pin 2 and 3 of the XLR should not have any continuity with the chassis, which is where you should have +48VDC from the phantom power switch connected via two 6k8 divider resistors.

I think you just need to do a thorough continuity test to see if you have any shorts. And also make sure that you are getting +48V at all of your phantom power switch poles when they are in the off position.

Thanks!

Paul

Click to expand...

Hi Paul,

I thought I had a problem with the xlr connectors, but the problem was with the 1/4 inputs I added.  The tip was connected to the input transformer, which was connected to  xlr input pin 3. Obviously an oversite on my part.  Thankfully the issue has been resolved and everything works great and sounds great. 

I had another issue which may help someone who is building their own power supply.  I had a bad lm317 that was giving me 24v unloaded.  When I connected to the pre, the voltage dropped.  That drove me crazy for about 30min before I discovered the bad lm317.  I tested the all transistors thinking I had a bad one before I thought about that damn regulator.
Paul,  thanks for your help.

Great news.

These are great sound preamps. Glad you now get to enjoy yours as well.

Thanks!

Paul

tomnyhbees said:

I thought I had a problem with the xlr connectors, but the problem was with the 1/4 inputs I added.  The tip was connected to the input transformer, which was connected to  xlr input pin 3. Obviously an oversite on my part.  Thankfully the issue has been resolved and everything works great and sounds great. 

Click to expand...

That mistake would not put 48V on the case, the tip should be connected to pin2, so what it could do is invert the polarity of the signal.

If you had 48V on the case then you connected the jack "Sleeve" (and not the tip) to Pin3

Whoops said:

That mistake would not put 48V on the case, the tip should be connected to pin2, so what it could do is invert the polarity of the signal.

If you had 48V on the case then you connected the jack "Sleeve" (and not the tip) to Pin3

Click to expand...

That correct, sleeve not pin.  Thanks

Hi,

I'm looking for some help troubleshooting one channel of my 4 channel 1290 build. 

All four channels have worked quite happily for some time, but recently I unintentionally left the unit powered on (with phantom applied to one channel) overnight.  The affected channel now inserts intermittent noise into the signal.  The other three channels are still fine.

I've isolated the problem to the area around TR1, having measured the following voltages:

TR1
B: 0.8v
C: 9.8v
E; 0.2v

TR2
B: 10.6v
C: 22.7v
E: 9.9v

So the problem looks to be the connection between the collector of TR1 and the base of TR2.  I wondered if leaving the unit powered on for so long might have cooked the polyester capacitor at C2, so I've replaced with a modern Wima, but no difference. 

I guess my next step would be to replace the transistors, but before I try that, am I on the right track?  Is there anything else I should consider in trying to resolve this problem?  The supply voltage is still accurate and the 68k resistor at R3 checks out fine.  All other transistor voltages are comparable to the working channels.

Any suggestions much appreciated!

Thanks,

Chris

Hi!
Are you talking about « crackle » noises, pop...?
I built a 4 units rack for 6 years now, many entires days of recording and had these symptoms two times...Each time I replaced 2n3055 and everything goes fine.

Hi,

Yes, the noise is crackles and pops.  I'll take a look at changing the 2n3055.  Is it possible that a failing 2n3055 could cause the off voltages at TR1 and TR2?

Thanks.

digistu said:

All four channels have worked quite happily for some time, but recently I unintentionally left the unit powered on (with phantom applied to one channel) overnight. 

Click to expand...

Neiher leaving the unit on or phantom power on have something to do with it.
A lot of Neve consoles and SSL consoles in studios are left always on, year after year.

digistu said:

I wondered if leaving the unit powered on for so long might have cooked the polyester capacitor at C2, so I've replaced with a modern Wima, but no difference. 

Click to expand...

Leaving the unit on will not cook any capacitor

Replace the 2N3055 and retouch all solder points, check voltages, it the voltages are fine you probably solved it

If it doesnt work replace all transistors

start from there

Hi there!
Buildin' for more ez1290 preamps...
Anyone experimented Carnhill VTB2280 (1+1:1+1) on output?
Cause I have spares 2280...
Wired parallel primaries/serie secondaries for 1:2 ratio, (narrow 1:1.7 ratio)

Is it working?

So if Iwanted a 1200  ohm input with the vtb9045, I would eliminate the jumper between pins 3 and 4, and then jumper pins 2 and  3, and 4 and 5?